Since X-rays have high substance transmittivity and can perform imaging with high spatial resolution, for example, X-rays are used for nondestructive inspection of subjects in industrial use, and for radiography in medical use. In these cases, a contrast image is formed by using a difference of X-ray absorption coefficient for substances, or living bodies when x-ray transmits through the substances or living bodies, depending on constituent elements or due to a difference in densities of the substances or living bodies. Such an imaging method is called X-ray absorption contrast method. However, a light element absorbs X-ray by a very small amount. It is difficult to image living soft tissues made of carbon, hydrogen, oxygen, etc., which are constituent elements of a living body, or soft materials by the X-ray absorption contrast method.
On the contrary to this, as a method for clearly imaging even tissues made of light elements, X-ray phase-contrast methods using a phase difference of X-rays have been studied since the nineteen-nineties.
A large number of X-ray phase-contrast methods have been developed. One of such methods may be an X-ray phase-contrast method using Talbot interference as a method capable of using a conventional X-ray tube (Patent literature 1).
The method using the Talbot interference described in Patent literature 1 includes an X-ray tube that generates X-rays, a phase grating that modulates the phase of the X-rays and generates an interference intensity distribution, an absorption grating that converts the interference intensity distribution into an intensity distribution of a Moiré, and an X-ray detector that detects the interference intensity distribution.
In the method described in Patent literature 1, imaging is performed by scanning the absorption grating along the direction of the grating period. With this scanning, the Moiré to be detected is moved. When the scanning length reaches one period of the absorption grating, the image of the Moiré is retrieved to the original state. Arithmetic processing is performed using at least three images of image data during scanning, and thus a differential phase image is acquired.
The method described in Patent literature 1 acquires a differential phase image by performing imaging for at least three images, and calculates a phase image from the differential phase image.
Since the method described in Patent literature 1 has to perform imaging for at least three images, if a subject is moved during imaging, image quality may be degraded.
Also, if the period of time for imaging increases, the X-ray dose for a subject increases. It is not desirable for medical use.
The present invention provides an X-ray imaging apparatus, an X-ray imaging method, and an X-ray imaging method that can acquire a differential phase image or a phase image of a subject by at least a single imaging operation.